1. Field of the Invention
The invention generally relates to the field of inkjet inks. More particularly, the invention relates to a gloss-controllable, radiation-curable inkjet ink.
2. Discussion of Related Technology
Radiation-curable inks enjoy a number of advantages over water- and solvent-based inks: they are reflected in their “green” or “environmentally friendly” nature and their other well-known advantages including: solvent-free formulation, near-instantaneous cure, improved coating performance, and single-pack system. Furthermore, the inks are cured by radiation after printing, and no extra energy and equipment are required to dry the inks, which meet the growing demand for greater efficiency and cost-effectiveness from the printing industry. For these reasons, their use continues to increase.
Radiation curing is a process whereby organic coatings such as inks are cured or hardened by exposure to electromagnetic radiation such as UV light. Because most radiation-curable inks are thermoset systems, after curing, they typically become hard or rigid as a result of the three-dimensional cross-linking that occurs between molecular chains.
Conventionally, radiation-curable inks include a polymerizable component containing an ethylenically unsaturated radiation-curable group, an initiator component such as a photo-initiator and optionally, a colorant component, such as a pigment, and an additive component.
Radiation-curable inks are generally composed of monomeric and oligomeric materials, pigments, initiators, and additives, and optionally, a small amount of solvent. Radiation-curable inks may be applied to numerous surfaces, both rigid and flexible, e.g. polyvinyl chloride (PVC), polystyrene, polycarbonate, acrylonitrile-butadiene-styrene (ABS), polyester, polyolefins, and textile materials. Ink properties such as adhesion, scratch and rub resistance, flexibility and such are primarily dependent on the properties of the polymerizable components, typically monomers and oligomers having an ethylenically unsaturated group, used in the ink. Most conventional radiation-curable inks have similar physical properties, such as adhesion and scratch resistance.
Conventionally, UV-curable inks use high percentages of poly-functional monomers or oligomers, which provide sufficient cross-linking, to formulate low-dosage UV-curable inks that are capable of rapid drying or curing of the ink dot using a small amount of energy. Because of their propensity to cross-link extensively in all spatial dimensions, such inks cure rapidly, resulting in a relatively rigid cured ink.
Conventionally, while high- and low-gloss inkjet inks are widely known, there are few, if any gloss-controllable radiation-curable inks.